Hot-Bar Soldering and Hot-Air Soldering for PAROLI®=Modules

Hot-Bar Soldering and Hot-Air Soldering for
PAROLI®=Modules
Appnote 76
by Arun Agarwal, updated by Elmar Dröge
Description
Overview of Surface Mount Soldering Methods
This technical note provides information on the two soldering
methods recommended for Infineon PAROLI (Parallel Optical
Link) modules: hot-bar soldering and hot-air soldering. Lead
frame technology is used for mounting PAROLI modules on the
printed circuit boards (PCBs). A lead frame is an etched or
punched array of metal traces or leads. The PAROLI circuit
board is attached to the lead frame at the inner portion of the
leads. The outer portion of the leads is used to attach the
PAROLI module to the next level of the assembly such as a
PCB.
Soldering is a process in which a solder paste is melted such
that it flows inbetween a lead of a device and a solder pad on a
PCB. After the subsequent cooling to room temperature and
hardening of the solder paste, a stable electric contact between
the device and the PCB is formed. Table 2 lists four soldering
methods with their typical expected temperatures.
Table 1 PAROLI Part Numbers
Infineon Part Number
Product Description
V23814-K1306-M230
12 Channel PAROLI DC Tx
V23815-K1306-M230
12 Channel PAROLI DC Rx
V23814-U1306-M130
12 Channel PAROLI AC Tx
V23815-U1306-M130
12 Channel PAROLI AC Rx
V23814-N1306-M130
12 Channel PAROLI AC Tx
V23815-N1306-M130
12 Channel PAROLI AC Rx
V23815-N1306-M150
12 Channel PAROLI AC Rx
The soldering methods, in which a PCB is placed into a forced
convection oven and all devices on the PCB are soldered in one
cycle need typical process temperatures of 236°C. With these
methods the case temperature of the devices is nearly identical
to the temperature at the solder pads and the device must
withstand these high temperatures.
Vapor phase soldering uses the vapor phase of a liquid for heating the solder paste (and the devices). As the temperature of a
vapor phase can be controlled precisely and is very homogeneous the process temperatures can be lowered. Still, case
temperatures as high as 217°C are used.
Hot-bar soldering is a process in which a heated bar simultaneously heats and solders all the leads of a device at one time,
the last two methods is that the temperature of the component
remains relatively low. They are, therefore, ideal technologies
for soldering parts that must be kept at reasonable temperatures.
Detail specifications of the PAROLI modules can be obtained
from Infineon Fiber Optics web site:
www.infineon.com/fiberoptics/
and selecting the topic “Parallel Optics”
Fiber Optics
PAROLI® is a registered trademark of Infineon Technologies AG.
JUNE 2000
bottom of the lead and the solder depots on the solder pad.
Table 2 Typical Soldering Methods and Associated Temperatures
Soldering Method
HotBar
Hot-Air Vapor Forced
Phase convection
methods
Temperature at PAROLI
leads
104°C
182°C
217°C
236°C
Maximum temperature
at solder pads
300°C
>207°C
217°C
236°C
PAROLI case temperature during soldering
30°C
123°C
217°C
236°C
Note: omitting the presoldering of the paste (steps 1 and 2)
can result in the leads pushing away the solder paste, which
would still be wet in this case. This will result in bad solder
joints.
5. Soldering using either hot-bar or hot-air soldering.
6. Cleaning of the PCB. This is only necessary if no low residue
flux is used. See also comments on PCB cleaning near the
end of this application note.
Temperature Profile for the Hot-Bar Soldering Step
Since it is strongly recommended that the PAROLI case temperature should not exceed 120°C during soldering, hot-bar soldering and hot-air soldering are the recommended methods for
soldering PAROLI modules onto the PCBs.
Hot-bar soldering entails heating a ceramic or metal blade
(often called a thermode) to a temperature high enough to activate flux and reflow solder. The edge of the blade is brought
down on to the device leads that are positioned on the PCB
pads. The hot thermode solders all the leads simultaneously
and uniformly. Figure 1 shows an example of the temperature
profile that can be used for PAROLI modules. It is recommended that the temperature profile be optimized to suit a specific application. Programmable systems with multistage heat
profiles are available from several suppliers. See the hot-bar
equipment supplier list at the end of this application note.
Hot-Bar and Hot-Air Soldering Processing Steps
The following steps for soldering PAROLI modules to a PCB are
recommended for both hot-bar and hot-air soldering. The two
methods differ only in the tools used in the soldering step:
blades (often called thermodes) are used for hot-bar soldering
and a hot-air nozzle is used for hot-air soldering.
1. Printing or dispensing of the solder paste on the PCB's solder
pads. The thickness of the solder paste should be approximately 100µm. It is recommended that the amount of dispensed solder paste be optimized to suit the specific
application.
Thermode Design for Hot-Bar Soldering
The thermode design plays a key role in providing heat transfer
and in keeping mechanical integrity during the soldering process. Lack of parallelism between the thermode and the leads
to be soldered may result in inconsistent transfer of heat and
poor solder joints. Figure 2 shows a schematic of the thermode
design for PAROLI modules. Guidelines for the thermode
dimensions are given in Figure 3. The tool dimensions have to
correspond to the PAROLI module dimensions (see PAROLI
data sheets). Therefore a tool consisting of three thermodes is
recommended. The tool has to provide enough space for the
PAROLI module in between the thermodes and has to ensure
overlap of the thermodes with all PAROLI leads and corresponding PCB solder pads. Exact tool dimensions (especially
the width of the thermodes) are dependent on the machinery
used. Please contact your hot-bar equipment supplier (see list
at the end of this application note).
2. Reflow soldering, using vapor phase, convection, or hot-air
process.
Steps 1 and 2 can be combined with a SMD process. After
step 2 the solder paste is presoldered on the PCB's solder
pads, forming hard deposits.
3. Application of flux.
4. Positioning of the PAROLI modules on the PCB and attaching
the modules with four screws from the back side of the PCB.
Please note that the PCB must have appropriate holes to
accommodate the PAROLI modules (see PAROLI data sheets
for dimensions). When the screws are tightened the PAROLI
leads are slightly bent, forming good contact between the
Figure 1 Typical thermal profile for hot-bar soldering
300oC
Temp at
Hot Bar
Tool
Temp 2
Tool Up
Temp 1
160oC
100oC
T2 = 5 s
T1 = 3 s
Slope 300oC/s
Stand-by
Stand-by
Bonding Cycle
Ambient
Time in Seconds
Fiber Optics
Hot-Bar Soldering and Hot-Air Soldering for PAROLI® Modules, Appnote 76
2
Figure 2 Schematic of a thermode design
Figure 3 Thermode dimension guidelines
16.4
3.0
(Module pillar)
18.7
2.2
0.9
10.9
Hot-Air Soldering Step
During the hot-air soldering step, flux and reflow solder are activated by the application of a hot-air stream through a nozzle (to
be more precise, most often it is a stream of hot nitrogen gas).
The procedure resembles that of hot-bar soldering: the nozzle is
brought down to the leads of the device that are positioned on
the PCB pads. Then the hot gas stream is turned on and solders all the leads simultaneously and uniformly. Figure 4 shows
the thermal profile for hot-air soldering with Finetech equipment that is used at Infineon. Other hot-air equipment suppliers
can provide the required expertise with their equipment (See
the list of hot-air equipment suppliers at the end of this application note).
The PAROLI case temperature (measured on the lower side of
the module) must not exceed 120°C, whereas the temperature
at the leads and solder pads has to exceed 207°C for 10 - 20
seconds to ensure proper reflow and good solder joints. These
two goals are achieved by the optimization of the following
parameters:
• Nozzle geometry
• Temperature of the gas stream
• Amount of gas flow
• Duration of the gas stream application
Process optimization can be done using mechanical samples of
PAROLI modules that can be provided by Infineon Technologies.
As a guideline for introducing a temperature profile for a hot-air
tool we recommend the following approach for process optimization:
Figure 4 Thermal profile for hot-air soldering with Fintech equipment
T2 = 15 s
360oC
T3 = 13.7 s
T1 = 3.7 s
Temp.
(tool
setting)
Slope 70oC/s
Stand-by
Stand-by
100oC
Bonding Cycle
Ambient
Time in Seconds
Fiber Optics
Hot-Bar Soldering and Hot-Air Soldering for PAROLI® Modules, Appnote 76
3
walls be designed asymmetrically. The side wall next to the
PAROLI module should be designed approximately 1.5mm
longer than the outer nozzle side wall (see Figure 6). This allows
the hot-air stream to flow across the leads and solder pads, and
then away from the PAROLI module. This helps to prevent the
accumulation of hot gas beneath the PAROLI module, which
would result in higher module case temperatures. Please contact your hot-air equipment supplier for tool details (see list at
the end of this application note).
Hot-Air Nozzle Design
Figure 5 shows a schematic of a sample nozzle design. Again,
design rules are dictated by the PAROLI module dimensions. A
nozzle with three rectangular openings is recommended. The
nozzle has to provide enough space for the PAROLI module to
be positioned between the openings and has to ensure overlap
of the nozzle openings with all PAROLI leads and corresponding
PCB solder pads. Exact nozzle dimensions are dependent on
the equipment selected. We recommend that the nozzle side
Figure 5 Schematic of the hot-air nozzle design
Figure 6 Detail of the hot-air nozzle sidewall
X 5:1
0.5
1.5
1.5
+0.2
0
2
Fiber Optics
Hot-Bar Soldering and Hot-Air Soldering for PAROLI® Modules, Appnote 76
4
result in an uneven solder reflow and bad solder joints. It is
therefore important that the PCB pads are designed properly.
Figure 7 shows some of the recommendations for the PCB layout.
Solder Pad Layout
PCB trace design and the amount of solder available on the
PCB pads may influence the temperature uniformity of the different solder pad-to-PAROLI lead connections during hot-bar or
hot-air soldering. This temperature non-uniformity may in turn
Figure 7 PCB trace layout recommendations
D e v ic e w ith le a d
fra m e
It is recommended that all pads should have the same size and
have a single trace contact. The traces connected to the pads
should have contractions just prior to the pads. A contraction of
at least 5x the width of the trace is recommended. This contraction will reduce heat flow from pads to the traces. The
same technique should be used for unused pads by connecting
them through a contraction to a trace length. Thermal sink
structures like ground connections and via holes should be
placed beyond the contractions. The goal is to create as identical a pad structure as possible to maintain temperature uniformity at the pads.
Temperature Limits
During the entire PAROLI soldering process, precautions should
be taken not to exceed PAROLI case temperature beyond
150°C.
PCB Cleaning
Special care should be taken to clean the PCB after hot-bar soldering of PAROLI modules. PAROLI modules are not hermetically sealed and water may get inside the modules if proper
care is not taken. The use of organic solvents, such as ketones
and ethers, are not recommended. It is advised that the solder
manufacturer be consulted about cleaning agents. We recommend the use of de-ionized water, ethanol and isopropyl alcohol. Hot air drying with temperatures that do not exceed 100°C
can be used. Ultrasonic baths are not recommended.
Solder Paste
Use of eutectic SnPb solder type is recommended for PAROLI
modules. Eutectic solder has a composition of 63% tin (Sn) and
37% lead (Pb), and has a eutectic temperature of 183oC. Low
residue flux is recommended.
Fiber Optics
Hot-Bar Soldering and Hot-Air Soldering for PAROLI® Modules, Appnote 76
5
Hot-Bar Soldering Equipment
Hot-Air Soldering Equipment
Hot-bar soldering equipment consists of a power supply unit, a
thermode, and a component positioning system. Both thermode and the positioning system are generally customized to
suit the application. The power supply is a standard unit and
comes with a variety of options and programming capabilities.
Most suppliers provide expertise in design and customization
of thermode and positioning systems for specific applications.
Some equipment suppliers are given here.
Hot-air soldering equipment consists of a heater, a gas flow
control, and a positioning system for the gas nozzle. Usually
only the gas nozzle is custom designed for the application.
Most suppliers provide expertise in design and customization
of the nozzle.
COVATEC SA
Rue des Artisan 11
CH-2503 Biel, Switzerland
Tel: +41-032-322-4550
UNITEK MIYACHI corp.
1820 S. Myrtle Ave.
Monrovia, CA 91017, USA
Tel: +1-626-358-8048
UME/WELD-EQUIP
Engelseweg 217, Postbus 164
NL-5700 AD Helmond, Netherlands
Tel: +31-492-542225
Some equipment suppliers are given here.
ZEVAC GmbH
Münchener Str. 22
D-85667 Oberpframmern
Tel: +49-8093 2055
AIR-VAC ENGINEERING COMPANY Inc.
30 Progress Avenue, P.O. Box 216,
Seymour, CN 06483, USA
Tel: +1-203-888-9900
FINETECH GmbH&Co. KG
Wolfener Str. 32/34, Haus 16
D-12681 Berlin
Tel: +49-30-936681-15
FINETECH
1334 E. Chandler Blvd. #5 D2,
Phoenix, AZ 85048, USA
Tel: +1-480-706-0551
Published by Infineon Technologies AG
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